Some sports and games, for example tennis, but also basketball, volleyball, handball, squash and many others, are played on a relatively small court with a special surface coating which has a major effect on the players' ease of movement at speeds and with accelerations or decelerations which can vary widely (including take-off, braking, sliding, engagement and re-engagement when strokes are played, and sudden changes of direction). Thus sports shoes are generally subject to intense stresses whose nature varies according to the court and the nature of the sport engaged in.
This has led to the development, at least for playing at top level, of shoes specialized for certain sports or types of sports, and sometimes, in the case of tennis for example, even for the nature of the playing surface. It is known that playing tennis on a clay court results in frequent sliding movements by the players which are clearly far greater and more abrasive than on other types of ground. Grass courts, which are clearly less damaging to soles than clay or hard surfaces, require special precautions for adhesion when wet. Many types of hard playing surfaces have also been developed which all have very specific properties of adhesion, abrasion, slip resistance and flexibility of contact.
The technology of sports shoes has thus developed considerably in recent years and manufacturers have diversified their ranges and offer innovative technical solutions for the production of soles.
French patent application 2 297 011 provides an example of a shoe in which, in order to increase wear resistance, the sole has a relatively compact continuous edge around the whole of its periphery, made from a material which is more abrasion-resistant than the central grooved part. Other designers (U.S. Pat. No. 4,134,220 for example) recommend specific materials and/or treatments to promote abrasion-resistance, or, as in U.S. Pat. No. 4,920,663, propose insertions or inclusions in certain sections of the sole for this purpose.
Clearly, as regards adhesion, manufacturers have traditionally made use of sculpted patterns formed by the alternation of solid areas and recesses on the surface of the sole, usually with the aim of creating in this way sharp edges which can increase the ease of adhesion of the sole to the playing surface. Thus, for example, European Patent EP 0 706 767 describes a sole which comprises in its surface a plurality of juxtaposed circular patterns, each pattern being composed of a small circular engagement section surrounded by a channel which is also circular. This results in a sole having a high “edge count” which theoretically provides elements for gripping or adhesion in all directions in its surface. Furthermore, the sole has a hollowed area in its thickness behind each engagement area and the corresponding channel, in such a way that the circular engagement area is suspended and can be pushed elastically towards the inside of the sole under the action of an engagement force perpendicular to the sole, thus providing automatic cleaning to remove the particles which have accumulated in the channel surrounding the area.
Patents EP 0 552 762 and JP 2004 216019 also describe embodiments of soles having straight ribs which are substantially parallel to each other in the direction perpendicular to the longitudinal direction of the shoe. The lateral flanks of these ribs are inclined towards the front of the shoe, in the direction from the ground contact surface towards the inside of the said sole, thus creating an edge which is less sharp than would be the case with a side perpendicular to the ground, and facilitating the forward slip of the shoe to a certain extent. Conversely, the rearward inclination of the rear lateral wall of each rib is substantially less than the forward inclination of its counterpart. The angle at the top of the corresponding edge is therefore more acute and offers greater resistance to the initiation of sliding of the rib in the direction from front to rear (the reverse direction). Certain parts of this sole may also be provided with longitudinal ribs.
It is also known, for example by the International PCT application No. WO99/38406, to provide a sports shoe sole with a rounded inner edge to increase the contact area, when compared with sharper edges, between the sole of the shoe and the ground as the sole tends to rotate during a lateral lunge of the player. Such transverse radius of curvature can be varied somewhat along the edge the keep this area from shrinking too much as one moves forwardly along the edge. Moreover this curved part of the sole in the inner forward portion of the shoe and around the edge thereof is cut with longitudinal channels with a distinct pattern over the tread pattern of the other parts of the sole.
In another embodiment of a sports shoe exemplified by UK patent application No. GB2136670, a plurality of castellated grooves are provided in a frontal area of the sole of a squash shoe, to increase flexibility of the same. In addition serrated edges and strips are provided in different areas under the sole to provide the gripping power where required.
Finally, patent application No. GB 2030039 depicts a sole for shoe for indoor sports with transverse parallel ribs exhibiting alternating sections of identical length but having two different widths. The tips of theses ribs are rounded in the surface of the sole. This provision is apparently designed to allow for some limited or controlled sliding capability. In one embodiment, two areas bordering opposite edges of the sole are provided with a pattern of concentric semi circular ribs exhibiting substantially the same features as depicted above, to allow for some pivoting movements of the sole.
Each of these different arrangements may allow a precise and specific performance objective to be achieved. However if one considers the bundle of performances which must be achieved today they are not adapted to meet the present requirement of top-level users. Indeed there is a requirement nowadays for a better compromise between the required or desirable minimum performance characteristics, which may conflict with each other, together with a sufficient service life with respect to wear, with allowance for the duration of matches or for economic constraints.